Quinone diimines show multiple functional activities useful to the rubber industry. A commonly used quinone-diimine, N-1,3-Dimethylbutyl-N'-phenyl-p-quinone diimine, is derived from the corresponding N-1,3-dimethylbutyl-N'-p-phenylene diamine via an oxidation reaction as follows: ##STR1##
Activities of quinone diimines which have been demonstrated as useful to the rubber and polymer industry include:
1.) Bound antioxidant, PA1 2.) Diffusable antiozonant, PA1 3.) PVI--process safety--delays scorch in new and reprocessed rubber, PA1 4.) Antioxidant for polymers and hydrocarbon liquids, PA1 5.) Polymerization Inhibitor for vinyl monomers. PA1 a) adding one or more elastomeric materials to a mixer; PA1 b) adding at least one quinone diimine antidegradant to the elastomeric material (s); PA1 c) mixing the combination of steps (a) and (b) for a period of about zero to about two minutes at an initial temperature of from about 60.degree. C. to about 100.degree. C.; PA1 d) adding carbon black, zinc oxide and stearic acid to the mixture of step (c) and continue mixing for about two to eight minutes or until the temperature reaches about 140.degree. C. to about 180.degree. C.; PA1 e) discharging the mixture of step (d) from the mixer; PA1 f) adding curatives, accelerators, processing aids, modifiers, tackifiers and conventional rubber processing aids;
Quinone diimines have been studied for use in various rubber technologies. In early studies, it was shown that after vulcanization of natural rubber or general-purpose elastomers in the presence of quinone diimines, a portion of the antidegradant is no longer extractable from the rubber. In addition, the remainder of the quinone diimine antidegradant is reduced to the commonly used p-phenylene diamine antiozonant. Corresponding experiments conducted with p-phenylene diamine antidegradants return nearly all of the antidegradant in its original form.
That the antioxidant is polymer bound has been demonstrated independently in experiments at the NRPA and at Voronezh Subsidiary of the All-Union Scientific Research Institute of Synthetic Rubber. (Raevsky et al., Kauch. Rezina, 29(3), pp. 9-10 (1970)). Raevsky et al. showed by ESR experiments that at least a portion the antidegradant becomes polymer bound and forms somewhat stable radicals. Synthetic poly(isoprene) was oxidized in the presence of quinone diimines. ESR signals were observed which correspond to those expected for the quinone diimine antidegradant. Even after re-precipitation in alcohol three times from solution in benzene, a reduced but persistent ESR signal was still observed. Since the polymer was re-precipitated, the authors concluded that the radicals must be chemically bonded to the polymer.
Perhaps Cain et al. (Rubber Industry, p. 216-226, 1975) gave better proof of the polymer bound nature of the antidegradant by demonstrating antioxidant activity that persisted even after solvent extraction. Cain tested vulcanizates protected with quinone imines or quinone diimines before and after hot methanol-acetone-chloroform azeotropic extraction. These vulcanizates showed antioxidant activity 2-30 times that of a control compound (unprotected azeotrope extracted vulcanizate).
Cain et al. compared the vulcanizate extraction experiments to monoalkene model studies. The results indicate that the additional products formed would indeed be bound to the polymer. Rubber parts are generally exposed to environmental factors such as heat, water, oils, and detergents causing losses of antidegradant through volatilization, and extraction or leaching mechanisms. Polymer-bound antidegradant will not be susceptible to these loss mechanisms. This persistent antioxidant activity demonstrated above should readily translate into long lasting antioxidant performance in rubber articles.
In order to observe the same level of antiozonant protection, the quinone diimine antidegradants require a higher loading than that of p-phenylene diamine antidegradants. This is to be expected when a portion of the antidegradant becomes bound to the polymer and is no longer diffusionally mobile. Ozone degradation occurs at the surface of the rubber. The antiozonant must be capable of migrating to the surface of the rubber in order to provide chemical or barrier protection.
Thus, prior to the present invention, quinone diimines were known as possessing antioxidant as well as antiozonant activity in the rubber polymer industry.